1. Field of the Invention
The present invention relates to selected phase change ink carrier compositions and phase change ink compositions containing those carrier compositions. In particular, the present claimed invention relates to a phase change ink composition containing a phase change ink carrier composition and at least one compatible colorant wherein the phase change ink carrier composition contains a Diels-Alder polymerization precursor (e.g. a dienophile) that is applied to a liquid intermediate transfer surface layer or directly onto a final receiving surface which contains a second Diels-Alder precursor (e.g. a diene). These Diels-Alder precursors react at temperatures from about 0.degree. C. to about 160.degree. C. to form a solid durable polymer at temperatures from about 20.degree. C. to 60.degree. C.
2. Brief Description of the Relevant Art
Phase change inks in digital printing applications (also sometimes called solid inks, or hot melt inks ) have in the past decade gained significant consumer acceptance as an alternative to more traditional printing systems such as offset printing, flexographic printing, gravure printing, letter press printing and the like. Phase change inks are especially desirable for the peripheral printing devices associated with computer technology, as well as being suitable for use in other printing technologies such as gravure printing applications as referenced in U.S. Pat. No. 5,496,879 and German Patent publications DE 4205636AL and DE 4205713AL assigned to Siegwerk Farbenfabrik Keller, Dr. Rung and Co.
In general, phase change inks are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the printing media or an intermediate transfer surface, they quickly solidify to form a predetermined pattern of solidified ink drops.
These solid inks are easy to use and safe. They can be easily loaded into the printer by the user, generally in the form of solid sticks of yellow, magenta, cyan and black ink having a solid consistency similar to children's crayons. Inside the printer, these inks are melted at an elevated temperature in a print head having a number of orifices, through which the melted ink will be ejected onto the desired final receiving substrate or media, such as paper or an overhead transparency film. Alternatively, the melted ink may be applied to a liquid coated rotating drum and then transferred to the substrate. As the ink cools on the substrate, it re-solidifies into the desired image. This resolidification process, or phase change, is instantaneous and a printed, dry image is thus made upon leaving the printer, which is available immediately to the user.
These phase change inks contain no solvents or diluents that can lead to undesired emissions. In all, the use and specific design of the phase change ink addresses many of the limitations of more traditional ink and printing processes. Specifically, the development of phase change inks has favorably addressed the environmental issues of source reduction, pollution prevention, emission standards, ground water contamination, airborne particulates, waste abatement, worker and consumer exposure, and non-reusable consumables.
Furthermore, because the ink is in cool, solid form at any time when the user can actually come in contact with the ink, and the ink is in a molten state only inside the printer and therefore inaccessible to the user, it is safe to use. These inks also have long-term stability for shipping and storage. Moreover, phase change inks are relatively safe to manufacture.
The phase change inks generally comprise a phase change ink carrier composition, which is combined with at least one compatible phase change ink colorant. The carrier composition has been generally composed of resins, fatty acid amides and resin derived materials. Also, plasticizers, waxes, antioxidants and the like have been added to the carrier composition. Generally the resins used are water-insoluble and the carrier composition contains no ingredients that are volatile at the jetting temperatures employed. Also, these carrier ingredients should be chemically stable so as not to lose their chemical identity over time and/or under elevated temperature conditions.
Preferably, a colored phase change ink will be formed by combining the above described ink carrier composition with compatible subtractive primary colorants. The subtractive primary colored phase change inks of this invention employ four component dyes, namely, cyan, magenta, yellow and black. U.S. Pat. Nos. 4,889,560 and 5,372,852 teach the subtractive primary colorants employed and typically may comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, C.I. Disperse Dyes, modified C.I. Acid and Direct Dyes, and a limited number of C.I. Basic Dyes. Also suitable as colorants are appropriate polymeric dyes, such as those described in U.S. Pat. No. 5,621,022 and those available from Milliken Chemical such as Milliken Ink Yellow 869, Milliken Ink Blue 92, Milliken Ink Red 357, Milliken Ink Yellow 1800, Milliken Ink Black 8915-67, uncut Reactint Orange X-38, uncut Reactint Blue X-17, and uncut Reactint Violet X-80 or those described in U.S. Pat. No. 5,231,135. Colored resin reaction products as described in U.S. patent application Ser. No. 08/672,617 filed Jun. 28, 1996 and assigned to the assignee of the present invention are also suitable colorants.
The specific choice of ingredients and their relative amounts is of critical importance in achieving the desired application performance properties of the phase change inks. Specific physical and chemical properties looked for in these inks include, but are not limited to viscosity, surface tension, flexibility, durability, thermal stability and the ability to deliver color.
In particular, two desired properties of phase change inks are (1) the durability of printed images and (2) the jettability of the ink to produce images on a substrate. Separately, polymeric materials are also added to the carrier composition to achieve the desired durability.
The following U.S. Patents teach specific phase change ink compositions.
U.S. Pat. No. 5,372,852 teaches that the selective phase change ink compositions described therein contain a phase change carrier composition comprising a fatty amide-containing material (either a tetra-amide compound or mono-amide or mixtures thereof). This patent further teaches the preferred tetra-amide compounds are made by reacting a fatty acid, a diamine (ethylene diamine) and a dimer acid. The preferred fatty acid is stearic acid and the preferred dimer acid is a hydrogenated oleic acid dimer product known as EMPOL 1008 Dimer Acid, manufactured by the Emery Division of Henkel Corporation of Cincinnati, Ohio. The preferred mono-amides are taught to be secondary mono-amides, such as behenyl behenamide and stearyl stearamide, products that are made under the KEMAMIDE trademark by Witco Chemical Company.
The pending U.S. patent application assigned to the assignee of the present invention discloses a number of urethane, urea, and mixed urethane/urea resins appropriate for use in phase change ink compositions, as do co-pending applications Ser. Nos. 08/672,816; 08/671,998; 08/672,815; 08/678,386 all filed on Jun. 28, 1996 and U.S. Pat. No. 5,750,064; all assigned to the assignee of the present invention.
While the phase change ink composition described by the above-noted U.S. Patents have met with great commercial success, there is always a need to improve those inks for more demanding processing conditions and different applications. Besides their performance on the printed substrates, inks and the individual components that go into them must be also measured by their cost and ease of manufacturing as well as how they work in a particular printer. Furthermore, the safety and environmental concerns for each component, as well as the ink in total, must be determined. The ideal phase change ink for a plain paper printer is one that encompasses the best qualities from all printing technologies.
Separately, the Diels-Alder reaction (also called the 4+2 cycloaddition reaction) is a well known technique for the synthesis of six membered rings. This reaction involves the 1,4-addition of the double bond of a dienophile to a conjugated diene to generate a six-membered ring. While this reaction has been used often to make relatively low molecular weight materials, it has been extended to polymeric materials. Furthermore, the selection of the diene and dienophile can include cyclic, heterocyclic and highly substituted materials containing complex functional groups and/or protected or latent functional groups. Diels-Alder adducts are typically stable.
Japanese Published Patent Application (Kokai) No. 07/61,117 (published on Mar. 7, 1995) teaches an ink jet recording method that uses a Diels-Alder reaction. However, this Diels-Alder reaction product is not a polymeric product.
Noriyuki Kuramoto et al. in "Thermoreversible Reaction of Diels-Alder Polymer Composed of Difurfurylapidate with Bismaleimidodiphenylmethane"; Journal of Polymer Science, Part A: Polymer Chemistry: Volume 32, pages 2501-2504 (1994) discusses several thermoreversible reactions of different Diels-Alder polymers as well as studies the subject reaction in detail. This class of polymers can be formed by a Diels-Alder reaction at 60.degree. C., yet will depolymerize by heating at 90.degree. C.
Co-pending U.S. patent application Ser. No. 09/065,378 filed Apr. 23, 1998, assigned to the assignee of the present invention teaches use of a thermally reversible Diels-Alder reaction to obtain printed image durability comparable to electrophotograhic imaging systems while avoiding the use of polymeric materials in the jetted ink.
However, none of the prior ink formulations possess the properties of a low viscosity liquid in the molten state and the properties of a non-thermally reversible polymer in the printed state while being implementable in a two component Diels-Alder reactive printing system.